Method and apparatus for transporting particles

Abstract: A method for transporting particles such as polyolefin particles from a first container (10) to a second container (12). The particles are transported from the first container to the second container through a transportation pipe (24) by means of pressure difference between the first container and the second container. A valve (26) is provided in the transportation pipe near the second container, and the valve is closed and opened to transmit particles intermittently. Cleaning gas is fed into the transportation pipe at a position on the inlet side near the valve. The cleaning gas is gas consisting essentially of olefin monomer. The cleaning gas is fed into the transportation pipe while the valve of the transportation pipe is closed, and the particles remained in the transportation pipe are made back to the first container thereby to clean the transportation pipe. Therefore, inside of the transportation pipe is kept clean all the time.

Description: The present invention relates to a method and an apparatus for transporting particles, such as polyolefin particles, through a pipe. It is a very important subject to prevent a pipe from being clogged with particles while particles are transported from one container to another container through the pipe. For example, when polyolefin particles are produced by a gas phase polymerization method in a primary reactor and transported to a secondary reactor in a next process or a storage tank through a transportation pipe, it is conventionally employed as one of transporting means that, after the particles are drawn from the reactor or the storage tank into a purge tank, a pressure difference between the purge tank and the following reactor or the storage tank is provided sufficiently to transport the particles at high speed. In the conventional method, the clogging of the transportation pipe is prevented by transporting polyolefin particles at high speed. However, this means is still unsatisfactory, and there is a tendency to clog the transportation pipe. There is a case that lump polymer is formed in the polymerization reactor in the reaction process. The lump polymer may stick and remain in the transportation pipe, which causes the clogging of the transportation pipe. Also, if the particles which have still reactive abilities remains in the pipe, the polymerisation reaction proceeds and the clogging of the pipe is occurred. Once the transportation pipe is clogged, starting from the clogged part, the clogging gets worse and worse. In this condition, the transportation pipe may be removed to take out the clogging objects. In result, it may unwillingly lead to shutdown of the polymerization reactor or cut of the production. US-A-4087134 discloses a method of transporting particles from a first container to a second container through a transportation pipe, the method comprising the steps of: providing a valve in laid transportation pipe; making the pressure in said first container higher than the pressure in said second container; closing and opening said valve to connect or disconnect the transportation pipe with atmosphere. The pressure of the first container is atmospheric and particles are conveyed from the first container to the second container in successive batches in a suction flow which is interrupted by opening the valve provided in the transportation pipe. Opening the valve communicates the pipe to atmosphere and interrupts the flow of particles upstream of the pipe while leaving the batches downstream of the valve under the influence of suction flow. By this means the speed of the individual batches can be kept low. It is an object of the present invention to provide a method and apparatus for transporting particles, without clogging of a transportation pipe. The invention provides a method of transporting particles from a first container to a second container through a transportation pipe, the method comprising the steps of: providing a valve in said transportation pipe; making the pressure in said first container higher than the pressure in said second container; closing and opening said valve to effect intermittent transport of particles from said first container to said second container; providing a supply source of cleaning gas to be supplied into said transportation pipe to clean inside of said transportation pipe; making the pressure of the cleaning gas supplied from said cleaning gas source higher than the pressure in said first container; supplying cleaning gas from said cleaning gas source into said transportation pipe while said valve is closed; and stopping the supply of cleaning gas from said cleaning gas source while said valve is open. Preferably, the method comprises the steps of providing a cleaning gas pipe between said cleaning gas source and said transportation pipe; providing a valve in said cleaning gas pipe; and closing and opening said valve to control the supply of cleaning gas into said transportation pipe. The valve may be provided in said transportation pipe near said second container. The cleaning gas may be fed into said transportation pipe at a position near said valve on the first container side. The valve may be provided in said transportation pipe near said first container. The cleaning gas may be fed into said transportation pipe at a position near said first valve on the second container side. Preferably, a difference between the pressure of said first container and the pressure of said second container is within a range of 1.5kg/cm 2 to 30kg/cm 2 and preferably within a range of 3kg/cm 2 to 15kg/cm 2 . Preferably, a difference between the pressure of cleaning gas supplied from said cleaning gas source and the pressure of said first container is at least 1.5kg/cm 2 and preferably at lease 2kg/cm 2 . The particles may be polyolefin and the cleaning gas may consist essentially of olefin monomer. The particles may be polypropylene and the cleaning gas may be a polypropylene gas. Each of said first container and said second container may be a reactor for gas phase polymerization or a storage tank therefor, with the proviso that said second container is said storage tank when said first container is said reactor. Advantageously, the duration of one continuous supply of said cleaning gas is 3 seconds or above. The invention also includes an apparatus for transporting particles, the apparatus comprising: a first container; a second container; a transportation pipe communicating between said first container and said second container; a first valve provided in said transportation pipe; and a control device for controlling said first valve such that said first valve is opened and closed to effect intermittent transport of particles from said first container to said second container, said apparatus further comprising a supply source of cleaning gas for cleaning inside of said transportation pipe; a cleaning gas pipe communicating between said cleaning gas source and said transportation pipe; and a second valve provided in said cleaning gas pipe; wherein said control device operates to control said first and second valves such that while said first valve is closed, said second valve is open to permit supply of the cleaning gas from said cleaning gas source into said transportation pipe, and while said first valve is open, said second valve is closed. The first valve may be provided in said transportation pipe near said second container. The cleaning gas pipe may be connected to said transportation pipe at a position near said first valve on the first container side. The first valve may be provided in said transportation pipe near said first container. The cleaning gas pipe may be connected to said transportation pipe at a position near said first valve on the second container side. Each of said first container and said second container may be a reactor for gas phase polymerization or a storage tank therefor, with the proviso that said second container is said storage tank when said first container is said reactor. The first and second valves may be solenoid valves. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the appended claims will become apparent to those skilled in the art from this detailed description. Fig. 1 is a view schematically showing the arrangement of a polypropylene production plant; ; and Fig. 2 is a flowchart showing the procedure of a method of transporting particles in that production plant. Referring now to Fig. 1, there is shown the arrangement of a polypropylene production plant. In Fig. 1, reference numeral 10 designates a primary fluidized-bed reactor, numeral 12 designates a secondary fluidized-bed reactor, and numeral 14 designates a storage tank. In the primary reactor 10, a mixed phase of gas comprising propylene monomer and polypropylene particles is formed, and fluidized by circulating gas from the bottom of the reactor 10 through a gas dispersion plate 16 placed in the lower part of the reactor 10 . Generally, the fluidized-bed which is rich in particle is formed in the lower part of the primary fluidized-bed reactor 10, and the gas phase which is rich in gas is formed in the upper part of the reactor 10. Gas is circulated by the operation of a compressor 20 provided in a pipe 18 which is connected to the primary reactor 10 in loop from the top to the bottom of the reactor 10. In the pipe 18, a cyclone 19 for separating entrained fine powder from circulation gas and a heat exchanger 21 for cooling circulation gas are placed. Under this state in which the mixed phase is fluidized, propylene monomer as a raw material through a pipe 22 and a catalyst through a pipe 23 are supplied to the primary reactor 10. Then polymerization reaction proceeds and particles of polypropylene are produced. Thus produced polypropylene particles in the primary reactor 10 are transported from fluidised-bed in the primary reactor 10 to gas phase in the secondary polymerization reactor 12 through a transportation pipe 24. Polypropylene particles are transported by means of pressure difference between the primary reactor 10 and the secondary reactor 12. This pressure difference is preferably within a range of 1.5kg/cm 2 -30kg/cm 2 . If the pressure difference is below 1.5kg/cm 2 , the transportation speed of particles is insufficient, and if the pressure difference is above 30kg/cm 2 , the vibration of the pipe 24 may increase. Especially, in the case of the polypropylene, in order to perform polymerization reaction and transportation of the particles successfully, it is important that a pressure difference between the container 1 and the container 2 is within a range of 1.5kg/cm 2 to 30kg/cm 2 . The more preferable range of the pressure difference between the reactors 10 and 12 is 3kg/cm 2 to 15kg/cm 2 . A solenoid valve 26 is placed in the transportation pipe 24 near the secondary reactor 12. In general, polypropylene particles are transported intermittently by opening and closing the valve 26. The construction of the secondary reactor 12 is substantially the same as that of the primary reactor 10. In other words, polypropylene particles are fluidized by gas circulated by a compressor 30 in a pipe 32. In the pipe 32, a cyclone 31 for separating entrained fine powder from circulation gas and a heat exchanger 33 for cooling circulation gas are placed. Then, polymerization reaction further proceeds by feeding raw material through a pipe 28, and polypropylene particles are produced as a product. Polypropylene particles as a product are transported from fluidized bed in the secondary reactor 12 to the storage tank 14 through the transportation pipe 34 by means of pressure difference between the secondary reactor 12 and the storage tank 14 and stored therein. Preferably, this pressure difference is within a range of 1.5kg/cm 2 -30kg/cm 2 . A solenoid valve 36 is placed in the transportation pipe 34 near the secondary reactor 12. In the same way as the transportation of particles from the primary reactor 10, particles are transported from the secondary reactor 12 intermittently by opening and closing the valve 36. Pressure sensors 38 and 40 are placed in the primary reactor 10 and the secondary reactor 12, respectively. The internal pressure of the reactors 10 and 12 is constantly monitored by a controller comprising, e.g., a micro computer 42. When the controller 42 detects the variation of the internal pressure of the reactors 38 and 40 based on signals from the pressure sensors 38 and 40, the controller 42 controls flow control valves 44 and 46 interposed in the pipes 22 and 28 to control flow of the raw material, thereby to maintain the internal pressure of the reactors 10 and 12 constant, respectively. In the embodiment shown in Fig. 1, one system is provided for feeding cleaning gas into the transportation pipes 24 and 34 in order to prevent a clogging object from being formed or to remove a clogging object, in the transportation pipes 24 and 34. This system comprises a source 50 for supplying the cleaning gas, and pipes 52, 54 and 56 for feeding cleaning gas from the cleaning gas source 50 into the transportation pipes 24 and 34. The pipe 54 is connected to the transportation pipe 24 between the primary reactor 10 and the secondary reactor 12 at a point 58 upstream of and near the valve 26. The pipe 56 is connected to the transportation pipe 34 between the secondary reactor 12 and the storage tank 14 at the point 60 on the downstream of and near the valve 36. Solenoid valves 62 and 64 are provided in the pipes 54 and 56, respectively. Reference numeral 66 in Fig. 1 is a pressure gauge placed in the pipe 52, and it is for measuring pressure of the cleaning gas from the cleaning gas source 50. The pressure of cleaning gas from the cleaning gas source 50 needs to be 1.5kg/cm 2 or above, preferably 2.0kg/cm 2 or above higher than the internal pressure of the reactors 10 and 12. If the difference between the pressure of the cleaning gas and the internal pressure of the reactors 10 and 12 is lower than 1.5kg/cm 2 , the cleaning gas would not have a cleaning function, which will be described later. Further, the cleaning gas is preferably gas consisting of propylene monomer, so as not to lower the efficiency of polymerization reaction in the reactor 10. Referring to Fig. 2, the transport of particles in the above-described arrangement will now be described. This is performed by controlling the valves 26, 36, 62 and 64 sequentially by a controller such as a sequencer 68 in the following way. Transportation of polypropylene particles from the primary reactor 10 to the secondary reactor 12 will be explained. First, as shown in Steps 100 and 102 of Fig. 2, the valve 26 in the transportation pipe 24 is closed, and immediately thereafter or at the same time, the valve 62 of the cleaning gas feeding system is opened. In result, the cleaning gas is fed from the supply source 50 to the transportation pipe 24 through the pipes 52 and 54. The cleaning gas flows in the transportation pipe 24 towards the primary reactor 10 to send the particles, and clogging objects if present, in the transportation pipe 24 into the primary reactor 10 thereby to clean the inside of the transportation pipe 24. Next, as shown in Step 104 of Fig. 2, the valve 62 is closed to stop the supply of cleaning gas. Immediately after the valve 62 is closed or at the same time, the valve 26 in the transportation pipe 24 is opened, and transportation of polypropylene particles from the primary reactor 10 to the secondary reactor 12 is started (Step 106). Duration of the valve 26 remained open is decided so as to adjust a difference between an actual amount of particles and a desired amount of particles, in the primary reactor 10. Although duration of the valve 62 or 64 remained open, i.e. duration of one continuous supply of cleaning gas may be changed according to lengths or a diameters of the pipes, it generally is 1 second or above, preferably 3 seconds or above, more preferably 5 seconds or above. Thereafter, a process goes back to step 100, and Steps 100-106 are repeated. The valve 62 is opened all the time when the valve 26 is closed. Further, similar to the transportation from the primary reactor 10, a product is transported from the secondary container 12 to the storage tank 14. In the case that the particles are transported from the secondary reactor 12 to the storage tank 14, cleaning gas may flow through the pipe 34 upstream, similar to the transportation from the primary reactor 10 to the secondary reactor 12. However, it is preferable to flow cleaning gas through pipe 34 downstream, thereby cleaning the inside of the pipe 34. Example 1 Polymerization reaction of propylene by gas phase method was conducted in a reactor which can produce 5 to 9 ton per hour of polypropylene, using solid catalyst component obtained by the same manner as in Example 1 in US-A-5,023,223, i.e. triethylaluminum and cyclohexylethyldimethoxysilane. Pressure in the primary reactor 10 was set to 21kg/cm 2 G, temperature therein to 75°C, pressure in the secondary reactor 12 to 17kg/cm 2 G and temperature therein to 75°C. A pipe which had an inner diameter of 50mm and a total length of 15m was used as a transportation pipe 24. The valve 26 was provided at a position separated from the entrance of the secondary reactor 12 by 20cm, and the pipe 54 was connected at a position on the upper stream of and near the valve 26. Propylene gas was used as cleaning gas and the pressure was 26kg/cm 2 G. Under these conditions, following Steps 100-106 in Fig. 2, the valves 24 and 62 were controlled and polypropylene was produced. After the plant ran for three consecutive months, the inside of the transportation pipe 24 was checked. In result, it was found that clogging did not occur in the transportation pipe 24. Example 2 The reaction was conducted under the same condition as the above-described example 1 except the valve 62 was closed all the time. In this case, the transportation pipe 24 was clogged after one hour or so and the plant was not able to run. Example 3 The reaction was conducted under the same condition as the above-described example 1 except propylene gas of 22.3kg/cm 2 G pressure was used as cleaning gas. In this case, a difference between the pressure of cleaning gas and the internal pressure of the primary reactor 10 was 1.3kg/cm 2 . In this example, it was found that clogging objects tended to be formed in the transportation pipe 24 within one or two days. The preferred embodiment of the present invention has been explained; however, it will be apparent that the present invention is not limited to the above embodiment. For example, the above embodiment relates to the transportation of polypropylene but the present invention can be applied to the transportation of polyethylene, polyolefin such as α-olefin polymer etc. In this case, cleaning gas is preferably gas consisting essentially of ethylene monomer or α-olefin monomer. In the above embodiment, there are two reactors. But if one reactor or three reactors are used, the present invention can be applied in such a case, which is obvious to one skilled in the art that the present invention can be applied in such a case. Although it is effective when the present invention is applied to a pipe for transporting polyolefin particles, the present invention can be applied to any type of pipes through which particles flow. Generally, particles to be transported have a diameter of 10µm-3000µm, preferably 100µm-2000µm and more preferably 200µm-1500µm, and a bulk density of 0.2g/cm 3 -1.0g/cm 3 and more preferably 0.3g/cm 3 -0.9g/cm 3 . Typically, these particles are transported through a pipe the inner surface of which is smooth and which has a diameter of 10mm-500mm and a length of 1m-200m, and to which the present invention can be applied. It will be understood that in the embodiment, the transportation pipes are cleaned by feeding the cleaning gas into the pipe, so that the clogging of the pipe can be prevented effectively and the inside of the pipe is kept clean all the time. Consequently, shut-down of the polymerization container or reactor or cut of production can be avoided. From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the appended claims.

Claims: A method of transporting particles from a first container (10; 12) to a second container (12; 14) through a transportation pipe (24; 34), the method comprising the steps of: providing a valve (26; 36) in said transportation pipe; making the pressure in said first container (10; 12) higher than the pressure in said second container (12; 14); closing and opening said valve (26; 36) to effect intermittent transport of particles from said first container to said second container; providing a supply source (50) of cleaning gas to be supplied into said transportation pipe to clean inside of said transportation pipe; making the pressure of the cleaning gas supplied from said cleaning gas source higher than the pressure in said first container; supplying cleaning gas from said cleaning gas source into said transportation pipe while said valve is closed; and stopping the supply of cleaning gas from said cleaning gag source while said valve (26; 36) is open. A method according to Claim 1, comprising the steps of providing a cleaning gas pipe (54; 56) between said cleaning gas source and said transportation pipe; providing a valve (62; 64) in said cleaning gas pipe; and closing and opening said valve (62; 64) to control the supply of cleaning gas into said transportation pipe (24; 34). A method according to Claim 1 or 2, wherein said valve (26) is provided in said transportation pipe (24) near said second container (12). A method according to Claim 3, wherein the cleaning gas is fed into said transportation pipe (24) at a position near said valve (26) on the first container side. A method according to Claim 1 or 2, wherein said valve (36) is provided in said transportation pipe (34) near said first container (12). A method according to Claim 5, wherein the cleaning gas is fed into said transportation pipe (34) at a position near said valve (36) on the second container side. A method according to any one of the preceding claims, wherein a difference between the pressure of said first container and the pressure of said second container is within a range of 1.5kg/cm 2 to 30kg/cm 2 and preferably within a range of 3kg/cm 2 to 15kg/cm 2 . A method according to any one of the preceding claims, wherein a difference between the pressure of cleaning gas supplied from said cleaning gas source (50) and the pressure of said first container is at least 1.5kg/cm 2 and preferably at least 2kg/cm 2 . A method according to any one of claims 1 to 8, wherein said particles are polyolefin. A method according to Claim 11, wherein said cleaning gas is gas consisting essentially of olefin monomer. A method according to any one of claims 1 to 8, wherein said particles are polypropylene. A method according to Claim 11, wherein said cleaning gas is propylene gas. A method according to any one of claims 9 to 12, wherein each of said first container and said second container is a reactor for gas phase polymerization or a storage tank therefor, with the provision that said second container is said storage tank when said first container is said reactor. A method according to any one of claims 1 to 13, wherein the duration of one continuous supply of said cleaning gas is 3 seconds or above. An apparatus for transporting particles, the apparatus comprising: a first container (10; 12); a second container (12; 14); a transportation pipe (24; 34) communicating between said first container (10; 12) and said second container (12; 14); a first valve (26; 36) provided in said transportation pipe (24; 34); and a control device (42) for controlling said first valve such that said first valve is opened and closed to effect intermittent transport of particles from said first container to said second container, said apparatus further comprising a supply source (50) of cleaning gas for cleaning inside of said transportation pipe; a cleaning gas pipe (54; 56) communicating between said cleaning gas source and said transportation pipe; and a second valve (62; 64) provided in said cleaning gas pipe; wherein said control device operates to control said first and second valves such that while said first valve is closed, said second valve is open to permit supply of the cleaning gas from said cleaning gas source into said transportation pipe, and while said first valve is open, said second valve is closed. A particles transporting apparatus according to Claim 15, wherein said first valve (26) is provided in said transportation pipe (24) near said second container (12). A particles transporting apparatus according to Claim 16, wherein said cleaning gas pipe (54) is connected to said transportation pipe (24) at a position near said first valve (26) on the first container side. A particles transporting apparatus according to Claim 15, wherein said first valve (36) is provided in said transportation pipe (34) near said first container (12). A particles transporting apparatus according to Claim 18, wherein said cleaning gas pipe (56) is connected to said transportation pipe (34) at a position near said first valve (36) on the second container side. A particles transporting apparatus according to any one of claims 15 to 19, wherein each of said first container and said second container is a reactor for gas phase polymerization or a storage tank therefor, with the proviso that said second container is said storage tank when said first container is said reactor. A particles transporting apparatus according to any one of claims 15 to 20, wherein said first and second valves are solenoid valves.

Inventors: HIRATA SEIJI, OGAWA HIROYUKI, SASAKI YOSHIZUMI, HIRATA, SEIJI, OGAWA, HIROYUKI, SASAKI, YOSHIZUMI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY LIMITED
Application year: 1994
Main classification: B65G53
IPC codes: B01J8, C08F10, B65G53